1. Field of the Invention
The present invention relates to a bifocus lens system capable of switching the focal length at the wide angle side and the telephoto side thereof and, and a portable machine using the same.
2. Description of the Prior Art
In recent years, it is becoming more and more common that a mobile phone (one example of the portable machine) is equipped with a device having image taking function. The portable machine perform imaging taking operation by the use of image taking lens assembly (optical system) and CCD (image sensor). Meanwhile, the image taking lens assembly no longer only has a single focus but must have an optical zoom function. However, the optical zoom contradicts the miniaturization of the portable machine. In addition, there will be many problems to be solved in terms of lens driving and cost.
Hereon, the present invention is not optical zoom but a bifocus lens system that is capable of switching the wide angle side and the telephoto side according to the focal length. The following are some citations regarding conventional art of the optical system for switching and replacing the focal length.
For example, JP Pat. No. 8122637 discloses an assistant lens, and JP Pat. No. 7318803 discloses a back surface switching lens, since it has an arbitrarily switchable device located at the image side of the chief lens system. However, it not only needs to arrange the assistant lens at the image side, but also has to use the CCD sensor, this makes it difficult to control the incident angle of the image side. Furthermore, the installation of assistant lens at the object side of the chief lens system is also of a known technology. However, in such condition, since the installation of the assistant lens increases the size of the lens, therefore, it is not ideal for the structure of a portable machine.
In addition, JP Pat. Nos. 5150192 and 720367 disclose an optical system that has a back surface switching lens disposed on the optical axis at the image side of the optical system, and such arrangement is of no help in improving the incident angle of the image side. Moreover, JP Pat. Nos. 6201993 and 7281092 disclose an optical system whose focal length is switched by a lens moveable along the optical axis. However, this condition should ensure a distance for the movable lens group, as a result, the total length of the optical system will have a problem. Therefore it is not suitable for the portable machine.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.